The procedure of mixed adhesives based on organic polyhydroxyl compounds and polyisocyanates is known (see for example British Pat. No. 1,408,510). One disadvantage of these types of adhesives is that, in order to obtain high cohesion strengths and thermal stability under load, it is necessary to use polyols and polyisocyanates having a high degree of branching. These products give adhesive films of limited flexibility and are therefore unsuitable for bonding flexible materials such as rubber or plastics. The addition of a plasticizer reduces the strength of cohesion. Although flexible adhesive films may be produced from polyols and polyisocyanates having a low degree of branching, the strength of cohesion thereof is very low. It has not been possible to satisfactorily obtain the requisite properties of flexible mixed adhesives by adding conventional inorganic or organic pigments.
It has now surprisingly been found that flexible bonds having outstanding cohesive strengths may be made on the known principle of two-component polyurethane adhesives, which contain a reaction mixture reacting to form polyurethane as an essential constituent, providing certain dispersions of polymers in organic hydroxyl compounds which will be more fully described below are used instead of the conventional polyhydroxyl compounds of polyurethane chemistry as reactants for the polyisocyanates. It has also been found that, by using these dispersions of polymers in polyhydroxyl compounds, it is also possible to make bonds based on isocyanate prepolymers which harden under the influence of moisture and which in turn may be obtained by reacting the above-mentioned dispersions with an excess of organic polyisocyanates.